Power management systems for multi engine rotorcraft

ABSTRACT

A power management system for a multi engine rotorcraft having a main rotor system with a main rotor speed. The power management system includes a first engine that provides a first power input to the main rotor system. A second engine selectively provides a second power input to the main rotor system. The second engine has at least a zero power input state and a positive power input state. A power anticipation system is configured to provide the first engine with a power adjustment signal in anticipation of a power input state change of the second engine during flight. The power adjustment signal causes the first engine to adjust the first power input to maintain the main rotor speed within a predetermined rotor speed threshold range during the power input state change of the second engine.

TECHNICAL FIELD OF THE DISCLOSURE

The present disclosure relates, in general, to power management systemsfor multi engine rotorcraft and, in particular, to power managementsystems operable to increase or decrease the power input of a mainrotorcraft engine in anticipation of a power input state change of asupplemental power unit during flight.

BACKGROUND

Many rotorcraft are capable of taking off, hovering and landingvertically. One such rotorcraft is a helicopter, which has a main rotorthat provides lift and thrust to the aircraft. The main rotor not onlyenables hovering and vertical takeoff and landing, but also enablesforward, backward and lateral flight. These attributes make helicoptershighly versatile for use in congested, isolated or remote areas. Thepower demand on the engine of a rotorcraft can vary over time based uponthe operation being performed. For example, an increased power demandmay be placed on the rotorcraft's engine during takeoff, hover, heavylifts and/or high speed operations.

Some rotorcraft utilize an auxiliary power unit to supply preflightpower during startup procedures and to start the main engine of therotorcraft. During high power demand operations, such an auxiliary powerunit may also serve as a supplemental power unit to provide supplementalpower to the main rotor. It has been found, however, that upon couplingthe supplemental power unit to the main rotor gearbox during flight, thesudden increase in power delivered to the main rotor may result in atemporary increase in rotor speed including the potential for rotoroverspeed. Likewise, it has been found, that upon decoupling thesupplemental power unit from the main rotor gearbox during flight, thesudden decrease in power delivered to the main rotor may result in atemporary decrease in rotor speed or rotor droop. Such undesired changesin rotor speed may predispose the rotorcraft to operational hazards andinefficiencies. Accordingly, a need has arisen for a power managementsystem for multi engine rotorcraft operable to maintain substantiallyconstant rotor speed during power input state changes associated withthe on demand use of a supplemental power unit during flight.

SUMMARY

In a first aspect, the present disclosure is directed to a powermanagement system for a multi engine rotorcraft having a main rotorsystem with a main rotor speed. The power management system includes afirst engine providing a first power input to the main rotor system. Asecond engine selectively provides a second power input to the mainrotor system. The second engine has at least a zero power input stateand a positive power input state. A power anticipation system isconfigured to provide the first engine with a power adjustment signalduring flight in anticipation of a power input state change of thesecond engine. The power adjustment signal causes the first engine toadjust the first power input to maintain the main rotor speed within apredetermined rotor speed threshold range during the power input statechange of the second engine.

In certain embodiments, the first engine may be a main engine and thesecond engine may be a supplemental power unit. In some embodiments, thefirst engine may be a first main engine and the second engine may be asecond main engine. In certain embodiments, the first engine may be agas turbine engine and the second engine may be a gas turbine engine. Insome embodiments, the first engine may be a gas turbine engine and thesecond engine may be an electric motor. In certain embodiments, thepower anticipation system may include a pilot operated input configuredto generate the power adjustment signal for the first engine and toprovide the second engine with a power input state change signal. Insome embodiments, the power anticipation system may include one or moresensors configured to detect one or more flight parameters of therotorcraft to form sensor data and a power anticipation moduleconfigured to generate the power adjustment signal for the first engineand to provide the second engine with the power input state changesignal responsive to the sensor data. In such embodiments, the sensordata may include collective control data, first engine speed data and/orfirst engine torque output data. In certain embodiments, the poweranticipation module may be implemented on a flight control computer.

In some implementations, the power adjustment signal may cause the firstengine to reduce the first power input coincident with the second enginechanging power input states from the zero power input state to thepositive power input state. In certain implementations, the poweradjustment signal may cause the first engine to increase the first powerinput coincident with the second engine changing power input states fromthe positive power input state to the zero power input state. In someembodiments, the power adjustment signal may cause an adjustment in thequantity of fuel injected into the first engine. In certain embodiments,the positive power input state of the second engine may include a fullpower input state. In some embodiments, the power adjustment signal maybe mechanically coupled to the first engine. In certain embodiments, thepower adjustment signal may be electrically coupled to the first engine.In some implementations, the predetermined rotor speed threshold rangemay be two percent above and below the main rotor speed, one percentabove and below the main rotor speed or other desired rotor speedthreshold range.

In a second aspect, the present disclosure is directed to a rotorcraftincluding a fuselage and a main rotor system rotatable relative to thefuselage. The main rotor system has a main rotor speed. A first engineprovides a first power input to the main rotor system. A second engineselectively provides a second power input to the main rotor system. Thesecond engine has at least a zero power input state and a positive powerinput state. A power anticipation system is configured to provide thefirst engine with a power adjustment signal during flight inanticipation of a power input state change of the second engine. Thepower adjustment signal causes the first engine to adjust the firstpower input to maintain the main rotor speed within a predeterminedrotor speed threshold range during the power input state change of thesecond engine.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the features and advantages of thepresent disclosure, reference is now made to the detailed descriptionalong with the accompanying figures in which corresponding numerals inthe different figures refer to corresponding parts and in which:

FIGS. 1A-1C are schematic illustrations of an exemplary multi enginerotorcraft utilizing a power management system in accordance withembodiments of the present disclosure;

FIGS. 2A-2B are block diagrams of a power management system operating ona multi engine rotorcraft in accordance with embodiments of the presentdisclosure;

FIGS. 3A-3B are graphical representations of main rotor speed versustime using a power management system on a multi engine rotorcraft inaccordance with embodiments of the present disclosure;

FIGS. 4A-4B are block diagrams of a power management system operating ona multi engine rotorcraft in accordance with embodiments of the presentdisclosure; and

FIGS. 5A-5D are block diagrams of a power management system operating ona multi engine rotorcraft in accordance with embodiments of the presentdisclosure.

DETAILED DESCRIPTION

While the making and using of various embodiments of the presentdisclosure are discussed in detail below, it should be appreciated thatthe present disclosure provides many applicable inventive concepts,which can be embodied in a wide variety of specific contexts. Thespecific embodiments discussed herein are merely illustrative and do notdelimit the scope of the present disclosure. In the interest of clarity,all features of an actual implementation may not be described in thisspecification. It will of course be appreciated that in the developmentof any such actual embodiment, numerous implementation-specificdecisions must be made to achieve the developer's specific goals, suchas compliance with system-related and business-related constraints,which will vary from one implementation to another. Moreover, it will beappreciated that such a development effort might be complex andtime-consuming but would nevertheless be a routine undertaking for thoseof ordinary skill in the art having the benefit of this disclosure.

In the specification, reference may be made to the spatial relationshipsbetween various components and to the spatial orientation of variousaspects of components as the devices are depicted in the attacheddrawings. However, as will be recognized by those skilled in the artafter a complete reading of the present disclosure, the devices,members, apparatuses, and the like described herein may be positioned inany desired orientation. Thus, the use of terms such as “above,”“below,” “upper,” “lower” or other like terms to describe a spatialrelationship between various components or to describe the spatialorientation of aspects of such components should be understood todescribe a relative relationship between the components or a spatialorientation of aspects of such components, respectively, as the devicesdescribed herein may be oriented in any desired direction. As usedherein, the term “coupled” may include direct or indirect coupling byany means, including by mere contact or by moving and/or non-movingmechanical connections.

Referring to FIGS. 1A-1C in the drawings, a rotorcraft in the form of ahelicopter is schematically illustrated and generally designated 10. Theprimary propulsion for helicopter 10 is a main rotor system 12. Mainrotor system 12 includes a plurality of rotor blades 14 extendingradially outward from a main rotor hub 16. Main rotor system 12 iscoupled to a fuselage 18 and is rotatable relative thereto. The pitch ofrotor blades 14 can be collectively and/or cyclically manipulated toselectively control direction, thrust and lift of helicopter 10. Acollective control 20 may be used to control the altitude and/or speedof helicopter 10 by simultaneously changing the pitch angle of all rotorblades 14 independently of their position. For example, during a stablehover, if pilot input is made to collective control 20, the pitch angleof all rotor blades 14 changes simultaneously and equally, resulting inhelicopter 10 either increasing or decreasing in altitude. A cycliccontrol 22 may be used to control the attitude and/or direction ofhelicopter 10 by controlling the pitch of rotor blades 14 cyclically,that is, the pitch of each rotor blade 14 will vary during eachrotation. The variation in pitch has the effect of varying the angle ofattack of, and thus the lift generated by, each rotor blade 14 as itrotates. Thus, if cyclic control 22 is moved forward or backward, mainrotor system 12 generates thrust in the forward direction or backwarddirection, respectively. Similarly, if cyclic control 22 is moved to theright or to the left, main rotor system 12 generates thrust in the rightdirection or left direction, respectively.

A tailboom 24 extends from fuselage 18 in the aft direction. Ananti-torque system 26 includes a tail rotor assembly 28 coupled to anaft end of tailboom 24. Anti-torque system 26 controls the yaw ofhelicopter 10 by counteracting the torque exerted on fuselage 18 by mainrotor system 12. In the illustrated embodiment, helicopter 10 includes avertical tail fin 30 that provide stabilization to helicopter 10 duringhigh speed forward flight. In addition, helicopter 10 includes wingmembers 32 a, 32 b that extend laterally from fuselage 18 and wingmembers 34 a, 34 b that extend laterally from tailboom 24. The wingmembers provide lift to helicopter 10 responsive to the forward airspeedof helicopter 10, thereby reducing the lift requirement on main rotorsystem 12 and increasing the top speed of helicopter 10

Main rotor system 12 and tail rotor assembly 28 receive torque androtational energy from a main engine 36. Main engine 36 is coupled to amain rotor gearbox 38 by suitable gearing, clutching and shafting. Mainrotor gearbox 38 is coupled to main rotor system 12 by a mast 40 and iscoupled to tail rotor assembly 28 by tail rotor drive shaft 42. Mainengine 36 may be an internal combustion engine such as a turbo shaftengine. In the illustrated embodiment, a supplemental power unit 44 iscoupled to main rotor gearbox 38 by suitable gearing, clutching andshafting. Supplemental power unit 44 may be an internal combustionengine such as a turbo shaft engine. Alternatively, supplemental powerunit 44 may be an electric motor.

Supplemental power unit 44 may operate as an auxiliary power unit toprovide preflight power to the accessories of helicopter 10 such aselectric generators, hydraulic pumps and the like as well as to providethe power required to start main engine 36. Supplemental power unit 44may also be operable to provide emergency power to main rotor system 12.For example, in the event of a failure of main engine 36, supplementalpower unit 44 is operable to provide emergency power to enhance theautorotation and flare recovery maneuver of helicopter 10. Use ofsupplemental power unit 44 not only enhances the safety of helicopter 10but also increases the efficiency of helicopter 10. For example, havingthe extra power provided by supplemental power unit 44 during high powerdemand operations allows main engine 36 to be downsized for moreefficient single engine operations such as during cruise operations.

Importantly, supplemental power unit 44 is operable to providesupplemental power that is additive with the power provided by mainengine 36 during, for example, takeoff, hover, heavy lifts, high speedoperations and other high power demand conditions. As stated herein,upon coupling a supplemental power unit to the main rotor gearbox duringflight, the sudden increase in power delivered to the main rotor mayresult in a temporary increase in rotor speed including the potentialfor rotor overspeed. Also, upon decoupling the supplemental power unitfrom the main rotor gearbox during flight, the sudden decrease in powerdelivered to the main rotor may result in a temporary decrease in rotorspeed or rotor droop. Such undesired changes in rotor speed maypredispose a rotorcraft to operational hazards and inefficiencies.Helicopter 10 implements a power management system that anticipatespower input state changes of supplemental power unit 44 and provides apower adjustment signal to main engine 36 to compensate for the suddenchanges in power provided by supplemental power unit 44, therebymaintaining main rotor system 12 at a substantially constant main rotorspeed.

Helicopter 10 is preferably a fly-by-wire rotorcraft that includes aflight control computer 46 implementing a variety of flight controlmodules including, for example, a power anticipation module 48. Poweranticipation module 48 utilizes pilot input and/or sensor input indetermining that a power input state change of supplemental power unit44 should occur. For example, if it is desired to cruise at a highspeed, the pilot may provide input to initiate the operation ofsupplemental power unit 44 from a zero power input state to a full powerinput state. As supplemental power unit 44 is preferable separated frommain gearbox 38 by a one-way clutch, the power input of supplementalpower unit 44 is not immediately available to main gearbox 38 whilesupplemental power unit 44 ramps up to full speed. When the operatingspeed of supplemental power unit 44 matches that of main gearbox 38,torque is now transferable through the one-way clutch. As supplementalpower unit 44 is now operable to provide full power, engagement ofsupplemental power unit 44 to main gearbox 38 delivers a sudden powerincrease rather than a gradual power increase. To compensate for thestep change in power delivered to main gearbox 38, power anticipationmodule 48 sends a power adjustment signal to main engine 36. In thepresent example, the power adjustment signal sent to main engine 36 frompower anticipation module 48 causes a reduction in the quantity of fuelinjected into main engine 36 which results in a decrease in the powerinput from main engine 36 that coincides with the increase in powerinput created by engaging supplemental power unit 44 with main gearbox38. By matching or substantially matching the power reduction of mainengine 36 with the power coming online from supplemental power unit 44,the power delivered to main gearbox 38 remains substantially constantsuch that the main rotor speed remains substantially constant and/orwithin a predetermined rotor speed threshold during engagement ofsupplemental power unit 44 with main gearbox 38 during flight.

In some implementations, power anticipation module 48 may autonomouslydetermine that a power input state change of supplemental power unit 44should occur responsive to acquired sensor data relating to one or moreflight parameters. For example, if it is desired to reduce the cruisespeed of helicopter 10 from a high speed regime in which supplementalpower unit 44 is operating in its full power input state and providing aportion of the total power to main rotor system 12, the pilot maydecrease collective to reduce the forward airspeed of helicopter 10. Oneor more sensors 50 that are operable to detect changes in various flightparameters such as collective position, main rotor actuator position,main engine torque, main engine RPMs, airspeed, altitude or otherparameter may provide sensor data to power anticipation module 48. Poweranticipation module 48 is in data communication with sensors 50 suchthat power anticipation module 48 may use the sensor data to determinewhether a power input state change of supplemental power unit 44 shouldoccur. In this example, responsive to the sensor data, poweranticipation module 48 sends a signal to supplemental power unit 44 totransition from its full power input state to its zero power inputstate.

As supplemental power unit 44 is preferable separated from main gearbox38 by a one-way clutch, as soon as the operating speed of supplementalpower unit 44 falls below that of main gearbox 38, torque is no longertransferable through the one-way clutch and supplemental power unit 44is operable to provide zero power to main gearbox 38. As such,disengagement of supplemental power unit 44 from main gearbox 38delivers a sudden power decrease rather than a gradual power decrease.To compensate for this step change in power delivered to main gearbox38, power anticipation module 48 also sends a power adjustment signal tomain engine 36. In the present example, the power adjustment signal sentto main engine 36 from power anticipation module 48 causes an increasein the quantity of fuel injected into main engine 36 which results in anincrease in the power input from main engine 36 that coincides with thedecrease in power caused by disengaging supplemental power unit 44 withmain gearbox 38. By matching or substantially matching the powerincrease of main engine 36 with the power coming offline fromsupplemental power unit 44, the power delivered to main gearbox 38remains substantially constant such that the main rotor speed remainssubstantially constant and/or within a predetermined rotor speedthreshold during disengagement of supplemental power unit 44 from maingearbox 38 during flight. Thus, the power management system implementedby helicopter 10 is operable to improve rotorcraft performance bypreventing overspeed and/or drooping of main rotor system 12 responsiveto power input state changes associated with the engagement ordisengagement of supplemental power unit 44.

It should be appreciated that helicopter 10 is merely illustrative of avariety of aircraft that can implement the embodiments disclosed herein.Indeed, the power management system of the present disclosure may beimplemented on any multi engine rotorcraft. Other aircraftimplementations can include hybrid aircraft, tiltwing aircraft,tiltrotor aircraft, quad tiltrotor aircraft, unmanned aircraft,gyrocopters, compound helicopters, drones and the like. As such, thoseskilled in the art will recognize that the power management system ofthe present disclosure can be integrated into a variety of aircraftconfigurations. It should be appreciated that even though aircraft areparticularly well-suited to implement the embodiments of the presentdisclosure, non-aircraft vehicles and devices can also implement theembodiments.

Referring to FIGS. 2A-2B in the drawings, various operatingconfigurations of a power management system 100 for a multi enginerotorcraft are illustrated in a block diagram format. Power managementsystem 100 includes a main engine 102 that may be an internal combustionengine such as a turbo shaft engine. Main engine 102 is coupled to afreewheeling unit depicted as sprag clutch 104 that acts as a one-wayclutch enabling a driving mode wherein torque from main engine 102 iscoupled to main rotor gearbox 106 via a combining gearbox 108 when theinput side rotating speed to sprag clutch 104 is matched with the outputside rotating speed from sprag clutch 104. For convenience ofillustration, the input side of sprag clutch 104 is depicted as the apexof the greater than symbol and the output side of sprag clutch 104 isdepicted as the open end of the greater than symbol. Importantly, spragclutch 104 has an over running mode wherein main engine 102 is decoupledfrom main rotor gearbox 106 when the input side rotating speed of spragclutch 104 is less than the output side rotating speed of sprag clutch104. Operating sprag clutch 104 in the over running mode allows, forexample, main rotor system 110 of helicopter 10 to engage inautorotation in the event of a failure of main engine 102.

In the illustrated embodiment, main rotor gearbox 106 is coupled to mainrotor system 110 by a suitable mast. Main rotor gearbox 106 includes agearbox housing and a plurality of gears, such as planetary gears, usedto adjust the engine output to a suitable rotational speed so that mainengine 102 and main rotor system 110 may each rotate at optimum speedduring flight operations of helicopter 10. Main rotor gearbox 106 iscoupled to a tail rotor gearbox 112 via a suitable tail rotor driveshaft. Tail rotor gearbox 112 includes a gearbox housing and a pluralityof gears that may adjust the main rotor gearbox output to a suitablerotational speed for operation of tail rotor 114.

Power management system 100 includes a secondary engine depicted as anauxiliary power unit and/or supplemental power unit that is referred toherein as supplemental power unit 116. In the illustrated embodiment,supplemental power unit 116 may be an internal combustion engine such asa turbo shaft engine. In the illustrated embodiment, supplemental powerunit 116 may generate between about 5 percent and about 40 percent ofthe horsepower of main engine 102 or other suitable percentage thereof.Supplemental power unit 116 is coupled to a freewheeling unit depictedas sprag clutch 118 that acts as a one-way clutch enabling a drivingmode wherein torque from supplemental power unit 116 is coupled to mainrotor gearbox 106 via combining gearbox 108 when the input side rotatingspeed to sprag clutch 118 is matched with the output side rotating speedfrom sprag clutch 118. Importantly, sprag clutch 118 has an over runningmode wherein supplemental power unit 116 is decoupled from main rotorgearbox 106 when the input side rotating speed of sprag clutch 118 isless than the output side rotating speed of sprag clutch 118. It isnoted that supplemental power unit 116 may be operable to perform thefunctions of a typical auxiliary power unit such as providing power todrive rotorcraft accessories such as one or more generators, one or morehydraulic pumps as well as other accessories (not pictured). Inaddition, supplemental power unit 116 may provide power for helicopter10 during the startup procedure and to start main engine 102.

Once main engine 102 is operating, torque is delivered through the maindrive system as indicated by the solid lines and arrowheads between mainengine 102, sprag clutch 104, combining gearbox 108, main rotor gearbox106, main rotor system 110, tail rotor gearbox 112 and tail rotor 114,as best seen in FIG. 2A. In the illustrated configuration, no torque isdelivered to combining gearbox 108 from supplemental power unit 116 asindicated by the dashed lines between supplemental power unit 116, spragclutch 118 and combining gearbox 108. As such, all of the power providedto main rotor system 110 is being provided by main engine 102 with zeropower being provided by supplemental power unit 116. It is noted thatsupplemental power unit 116 may continue to perform the functions of atypical auxiliary power unit and/or main engine 102 may provide power todrive rotorcraft accessories.

The operations of engaging and disengaging supplemental power unit 116to and from main gearbox 106 will now be described. Power managementsystem 100 includes a power anticipation system 120 that may be pilotimplemented and/or may be automated by the flight control computer 46 ofhelicopter 10 via a power anticipation module 48 executing poweranticipation logic. In FIG. 2A, main engine 102 is providing all of thepower to rotate main rotor system 110 and main rotor system 110 ispreferably rotating a constant main rotor speed as indicated by line 130in FIG. 3A that represents the nominal 100 percent main rotor speed. Ifit is desired to increase the cruise speed of helicopter 10 from astandard cruise regime to a high speed cruise regime, power anticipationsystem 120, responsive to pilot input and/or sensor input, may initiatea power input state change sequence for helicopter 10. In theillustrated embodiment, power anticipation system 120 sends a poweradjustment signal to main engine 102 and sends a power input statechange signal to supplemental power unit 116. For example, the poweradjustment signal to main engine 102 may be a mechanically coupledsignal to the throttle of main engine 102 causing a decrease in fuelinjected into main engine 102. Alternatively, the power adjustmentsignal to main engine 102 may be an electrically coupled signal to mainengine 102 causing a decrease in fuel injected into main engine 102.

The power input state change signal to supplemental power unit 116transitions supplemental power unit 116 from a zero power input state toa full power input state. For example, supplemental power unit 116 maytransition from a non-operating state, an operating in idle mode stateor otherwise operating at a speed below which the input side rotatingspeed of sprag clutch 118 is less than the output side rotating speed ofsprag clutch 118. The power input state change signal causessupplemental power unit 116 to ramp up and engage main rotor gearbox 106when the operating speed of supplemental power unit 116 causes the inputside rotating speed of sprag clutch 118 to match the output siderotating speed of sprag clutch 118. Without power anticipation system120 sending the power adjustment signal to main engine 102, the mainrotor speed would temporarily increase, as indicated by line 132 in FIG.3A, responsive to the sudden increase in power to main rotor system 110.In the present embodiments, however, the power adjustment signal sent tomain engine 102 causes a coincident reduction in power from main engine102 as the step change in power from supplemental power unit 116 isdelivered.

The reduction in power from main engine 102 compensates for the increasein power from supplemental power unit 116 such that the main rotor speedremains substantially constant, as indicated by line 130 in FIG. 3A,such as between an upper rotor speed threshold 134 and a lower rotorspeed threshold 136. In one implementation, upper rotor speed threshold134 may be set at 102 percent of main rotor speed 130 and lower rotorspeed threshold 136 may be set at 98 percent of main rotor speed 130forming a rotor speed threshold range of two percent above and twopercent below main rotor speed 130. In another implementation, upperrotor speed threshold 134 may be set at 101 percent of main rotor speed130 and lower rotor speed threshold 136 may be set at 99 percent of mainrotor speed 130 forming a rotor speed threshold range of one percentabove and one percent below main rotor speed 130. Even though particularrotor speed threshold ranges have been described, it should beunderstood by those having ordinary skill in the art that rotor speedthreshold ranges may be set to any desired value to optimize systemdesign including ranges greater than or less than those recited herein.Once supplemental power unit 116 is operating at full speed, torque isdelivered, not only, through the main drive system as indicated by thesolid lines and arrowheads between main engine 102, sprag clutch 104,combining gearbox 108, main rotor gearbox 106 and main rotor system 110,but also, through a supplemental drive system as indicated by the solidlines and arrowheads between supplemental power unit 116, sprag clutch118 and combining gearbox 108, as best seen in FIG. 2B.

When it is desired to decrease the cruise speed of helicopter 10 fromthe high speed cruise regime, power anticipation system 120, responsiveto pilot input and/or sensor input, may initiate a power input statechange sequence for helicopter 10. In the illustrated embodiment, poweranticipation system 120 sends a power adjustment signal to main engine102 and sends a power input state change signal to supplemental powerunit 116. The power adjustment signal to main engine 102 may be amechanically coupled or electrically coupled signal causing an increasein fuel injected into main engine 102.

The power input state change signal to supplemental power unit 116transitions supplemental power unit 116 from the full power input stateto a zero power input state. For example, supplemental power unit 116may transition to an operating speed such that the input side rotatingspeed of sprag clutch 118 is less than the output side rotating speed ofsprag clutch 118, thus decoupling torque to and disengaging from mainrotor gearbox 106. Without power anticipation system 120 sending thepower adjustment signal to main engine 102, the main rotor speed wouldtemporarily decrease, as indicated by line 142 in FIG. 3B, responsive tothe sudden decrease in power to main rotor system 110. In the presentembodiments, however, the power adjustment signal sent to main engine102 causes a coincident increase in power from main engine 102 as thestep change in power from supplemental power unit 116 is received.

The increase in power from main engine 102 compensates for the decreasein power from supplemental power unit 116 such that the main rotor speedremains substantially constant, as indicated by line 140 in FIG. 3B,such as between an upper rotor speed threshold 144 and a lower rotorspeed threshold 146. In one implementation, upper rotor speed threshold144 may be set at 102 percent of main rotor speed 140 and lower rotorspeed threshold 146 may be set at 98 percent of main rotor speed 140forming a rotor speed threshold range of two percent above and twopercent below main rotor speed 140. In other implementations, the rotorspeed threshold range may have any desired value to optimizeperformance. Once supplemental power unit 116 is disengaged, torque isdelivered exclusively through the main drive system as indicated by thesolid lines and arrowheads between main engine 102, sprag clutch 104,combining gearbox 108, main rotor gearbox 106 and main rotor system 110,and the dashed lines between supplemental power unit 116, sprag clutch118 and combining gearbox 108, as best seen in FIG. 2A.

Even though the upper rotor speed threshold and the lower rotor speedthreshold have been described as having the same deviation from thenominal main rotor speed, it should be understood by those havingordinary skill in the art that an upper rotor speed threshold could havea different deviation from the nominal main rotor speed than a lowerrotor speed threshold. Also, even though the upper rotor speed thresholdand the lower rotor speed threshold have been described as being thesame during engagement and disengagement of supplemental power, itshould be understood by those having ordinary skill in the art that theupper and lower rotor speed thresholds could be different depending uponthe flight operation being conducted. In addition, even though the powerinput state changes have been described as transitions between a fullpower input state and a zero power input state of a supplemental powerunit, it should be understood by those having ordinary skill in the artthat the benefits of implementing a power management system of thepresent disclosure can also be achieved when transitioning between otherpower input states including any number of intermediate power inputstates between the full power input state and the zero power input statesuch as a quarter power input state, a half power input state, a threequarter power input state or other positive power input statetherebetween.

Even though the power anticipation system functionality has beendescribed with reference to a multi engine rotorcraft having a mainengine and a supplemental power unit, it should be understood by thosehaving ordinary skill in the art that a power anticipation system of thepresent disclosure may have benefits on other multi engine rotorcraft.For example, as best seen in FIGS. 4A-4B of the drawings, a powermanagement system 200 is operating in a twin engine rotorcraft. Powermanagement system 200 includes a first main engine 202 such as a turboshaft engine that is coupled to a freewheeling unit depicted as spragclutch 204 that acts as a one-way clutch enabling a driving mode whereintorque from main engine 202 is coupled to main rotor gearbox 206 via acombining gearbox 208 and an over running mode wherein main engine 202is decoupled from main rotor gearbox 206. In the illustrated embodiment,main rotor gearbox 206 is coupled to main rotor system 210 by a suitablemast. Main rotor gearbox 206 is coupled to a tail rotor gearbox 212 viaa suitable tail rotor drive shaft. Tail rotor gearbox 212 is coupled toa tail rotor 114. Power management system 200 includes a second mainengine 216 such as a turbo shaft engine that is coupled to afreewheeling unit depicted as sprag clutch 218 that acts as a one-wayclutch enabling a driving mode wherein torque from main engine 216 iscoupled to main rotor gearbox 206 via combining gearbox 208 and an overrunning mode wherein main engine 216 is decoupled from main rotorgearbox 206.

In certain flight operations such as high efficiency cruise, main engine202 may be operating to provide torque through the drive system asindicated by the solid lines and arrowheads between main engine 202,sprag clutch 204, combining gearbox 208, main rotor gearbox 206, mainrotor system 210, tail rotor gearbox 212 and tail rotor 214, while mainengine 216 is not providing torque through the drive system as indicatedby the dashed lines between main engine 216, sprag clutch 218 andcombining gearbox 208, as best seen in FIG. 4A. If it is desired totransition from high efficiency cruise to high speed cruise, poweranticipation system 220, responsive to pilot input and/or sensor input,may initiate a power input state change sequence for the twin enginerotorcraft. For example, power anticipation system 220 sends a poweradjustment signal to main engine 202 and sends a power input statechange signal to main engine 216. The power input state change signaltransitions main engine 216 from a zero power input state to a positivepower input state such as a full power input state or other desiredpercentage of the full power input state. The power input state changesignal causes main engine 216 to ramp up and engage main rotor gearbox206. The power adjustment signal sent to main engine 202 causes acoincident reduction in power from main engine 202 as the step change inpower from main engine 216 is delivered, thereby maintaining the mainrotor speed substantially constant, such as within upper and lower rotorspeed thresholds. Once main engine 216 is engaged, torque is providedthrough the main drive system as indicated by the solid lines andarrowheads between main engine 202, sprag clutch 204, combining gearbox208, main rotor gearbox 206 and main rotor system 210, as well asbetween main engine 216, sprag clutch 218 and combining gearbox 208, asbest seen in FIG. 4B.

If it is desired to return to high efficiency cruise, power anticipationsystem 220, responsive to pilot input and/or sensor input, may initiatea power input state change sequence for the twin engine rotorcraft. Inthis case, power anticipation system 220 sends a power adjustment signalto main engine 202 and sends a power input state change signal to mainengine 216. The power input state change signal transitions main engine216 from the positive power input state to a zero power input state. Thepower adjustment signal sent to main engine 202 causes a coincidentincrease in power from main engine 202 as the step change in power frommain engine 216 is received, thereby maintaining the main rotor speedsubstantially constant, such as within upper and lower rotor speedthresholds. Once main engine 216 is disengaged, torque is deliveredthrough the main drive system as indicated by the solid lines andarrowheads between main engine 202, sprag clutch 204, combining gearbox208, main rotor gearbox 206 and main rotor system 210, with no torqueprovided from main engine 216 as indicated by the dashed lines betweenmain engine 216, sprag clutch 218 and combining gearbox 208, as bestseen in FIG. 4A. It is noted that the twin engine rotorcraft couldalternatively be returned to high efficiency cruise mode by disengagingmain engine 202 and exclusively operating main engine 216 in which case,power anticipation system 220 would send the power adjustment signal tomain engine 216 and the power input state change signal to main engine202.

Even though the power anticipation system functionality has beendescribed with reference to a multi engine rotorcraft having two turboshaft engines, it should be understood by those having ordinary skill inthe art that a power anticipation system of the present disclosure mayhave benefits on rotorcraft utilizing hybrid power systems. For example,as best seen in FIGS. 5A-5D of the drawings, a power management system300 is operating in a twin engine hybrid rotorcraft. Power managementsystem 300 includes a turbo generator 302 such as a turbo shaft enginethat is coupled to or integral with an electric generator. Turbogenerator 302 is coupled to a freewheeling unit depicted as sprag clutch304 that acts as a one-way clutch enabling a driving mode wherein torquefrom turbo generator 302 is coupled to main rotor gearbox 306 via acombining gearbox 308 and an over running mode wherein turbo generator302 is decoupled from main rotor gearbox 306. In the illustratedembodiment, main rotor gearbox 306 is coupled to main rotor system 310by a suitable mast. Main rotor gearbox 306 is coupled to a tail rotorgearbox 312 via a suitable tail rotor drive shaft. Tail rotor gearbox312 is coupled to a tail rotor 314. Power management system 300 includesan electric motor 316 coupled to one or more batteries and/or thegenerator of turbo generator 302. In the illustrated embodiment,electric motor 316 is coupled to a freewheeling unit depicted as spragclutch 318 that acts as a one-way clutch enabling a driving mode whereintorque from electric motor 316 is coupled to main rotor gearbox 306 viacombining gearbox 308 and an over running mode wherein electric motor316 is decoupled from main rotor gearbox 306. In other embodiments,sprag clutch 318 may be optional in which case, electric motor 316 maybe coupled directly to combining gearbox 308.

In certain flight operations such as high efficiency cruise, turbogenerator 302 may be operating to provide torque through the drivesystem as indicated by the solid lines and arrowheads between turbogenerator 302, sprag clutch 304, combining gearbox 308, main rotorgearbox 306, main rotor system 310, tail rotor gearbox 312 and tailrotor 314, while electric motor 316 is not providing torque through thedrive system as indicated by the dashed lines between electric motor316, sprag clutch 318 and combining gearbox 308, as best seen in FIG.5A. If it is desired to transition from high efficiency cruise to highspeed cruise, power anticipation system 320, responsive to pilot inputand/or sensor input, may initiate a power input state change sequencefor the twin engine hybrid rotorcraft. For example, power anticipationsystem 320 sends a power adjustment signal to turbo generator 302 andsends a power input state change signal to electric motor 316. The powerinput state change signal transitions electric motor 316 from a zeropower input state to a positive power input state such as a full powerinput state or other desired percentage of the full power input state.The power input state change signal causes electric motor 316 to ramp upand engage main rotor gearbox 306. The power adjustment signal sent toturbo generator 302 causes a coincident reduction in power from turbogenerator 302 as the step change in power from electric motor 316 isdelivered, thereby maintaining the main rotor speed substantiallyconstant, such as within upper and lower rotor speed thresholds. Onceelectric motor 316 is engaged, torque is provided through the main drivesystem as indicated by the solid lines and arrowheads between turbogenerator 302, sprag clutch 304, combining gearbox 308, main rotorgearbox 306 and main rotor system 310, as well as between electric motor316, sprag clutch 318 and combining gearbox 308, as best seen in FIG.5B.

If it is desired to engage in high efficiency electric powered cruise,power anticipation system 320, responsive to pilot input and/or sensorinput, may initiate a power input state change sequence for the twinengine hybrid rotorcraft. In this case, power anticipation system 320sends a power adjustment signal to electric motor 316 and sends a powerinput state change signal to turbo generator 302. The power input statechange signal transitions turbo generator 302 from the positive powerinput state to a zero power input state. The power adjustment signalsent to electric motor 316 causes a coincident increase in power fromelectric motor 316 as the step change in power from turbo generator 302is received, thereby maintaining the main rotor speed substantiallyconstant, such as within upper and lower rotor speed thresholds. Onceturbo generator 302 is disengaged, torque is delivered through the maindrive system as indicated by the solid lines and arrowheads betweenelectric motor 316, sprag clutch 318, combining gearbox 308, main rotorgearbox 306 and main rotor system 310, with no torque provided fromturbo generator 302 as indicated by the dashed lines between turbogenerator 302, sprag clutch 304 and combining gearbox 308, as best seenin FIG. 5C.

If it is desired to transition from high efficiency electric poweredcruise to high speed cruise, power anticipation system 320, responsiveto pilot input and/or sensor input, may initiate a power input statechange sequence for the twin engine hybrid rotorcraft. For example,power anticipation system 320 sends a power adjustment signal toelectric motor 316 and sends a power input state change signal to turbogenerator 302. The power input state change signal transitions turbogenerator 302 from a zero power input state to a positive power inputstate such as a full power input state or other desired percentage ofthe full power input state. The power input state change signal causesturbo generator 302 to ramp up and engage main rotor gearbox 306. Thepower adjustment signal sent to electric motor 316 causes a coincidentreduction in power from electric motor 316 as the step change in powerfrom turbo generator 302 is delivered, thereby maintaining the mainrotor speed substantially constant, such as within upper and lower rotorspeed thresholds. Once turbo generator 302 is engaged, torque isprovided through the main drive system as indicated by the solid linesand arrowheads between turbo generator 302, sprag clutch 304, combininggearbox 308, main rotor gearbox 306 and main rotor system 310, as wellas between electric motor 316, sprag clutch 318 and combining gearbox308, as best seen in FIG. 5D.

The flight control computers of the present embodiments preferablyinclude computing elements such as non-transitory computer readablestorage media that include computer instructions executable byprocessors for controlling flight operations. The computing elements maybe implemented as one or more general-purpose computers, special purposecomputers or other machines with memory and processing capability. Thecomputing elements may include one or more memory storage modulesincluding, but is not limited to, internal storage memory such as randomaccess memory, non-volatile memory such as read only memory, removablememory such as magnetic storage memory, optical storage, solid-statestorage memory or other suitable memory storage entity. The computingelements may be implemented as microprocessor-based systems operable toexecute program code in the form of machine-executable instructions. Thecomputing elements may be selectively connectable to other computersystems via a proprietary encrypted network, a public encrypted network,the Internet or other suitable communication network that may includeboth wired and wireless connections.

The foregoing description of embodiments of the disclosure has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the disclosure to the precise formdisclosed, and modifications and variations are possible in light of theabove teachings or may be acquired from practice of the disclosure. Theembodiments were chosen and described in order to explain the principalsof the disclosure and its practical application to enable one skilled inthe art to utilize the disclosure in various embodiments and withvarious modifications as are suited to the particular use contemplated.Other substitutions, modifications, changes and omissions may be made inthe design, operating conditions and arrangement of the embodimentswithout departing from the scope of the present disclosure. Suchmodifications and combinations of the illustrative embodiments as wellas other embodiments will be apparent to persons skilled in the art uponreference to the description. It is, therefore, intended that theappended claims encompass any such modifications or embodiments.

What is claimed is:
 1. A power management system for a multi enginerotorcraft having a main rotor system with a main rotor speed, the powermanagement system comprising: a first engine providing a first powerinput to the main rotor system; a second engine selectively providing asecond power input to the main rotor system, the second engine having atleast a zero power input state and a positive power input state; acombining gearbox coupling the first and second engines to the mainrotor system; a sprag clutch having an input side coupled to the secondengine and an output side coupled to the combining gearbox, the spragclutch configured to generate power input step changes between the zeropower input state and the positive power input state when a rotatingspeed of the input side transitions above or below a rotating speed ofthe output side; and a power anticipation system configured to providethe first engine with a power adjustment signal in anticipation of thepower input step changes; wherein, the power adjustment signal causesthe first engine to adjust the first power input coincident with thepower input step changes to maintain the main rotor speed within apredetermined rotor speed threshold range.
 2. The power managementsystem as recited in claim 1 wherein the first engine further comprisesa main engine and wherein the second engine further comprises asupplemental power unit.
 3. The power management system as recited inclaim 1 wherein the first engine further comprises a first main engineand wherein the second engine further comprises a second main engine. 4.The power management system as recited in claim 1 wherein the firstengine further comprises a first gas turbine engine and wherein thesecond engine further comprises a second gas turbine engine.
 5. Thepower management system as recited in claim 1 wherein the first enginefurther comprises a gas turbine engine and wherein the second enginefurther comprises an electric motor.
 6. The power management system asrecited in claim 1 wherein the power anticipation system furthercomprises a pilot operated input configured to generate the poweradjustment signal for the first engine and to provide the second enginewith a power input state change signal.
 7. The power management systemas recited in claim 1 wherein the power anticipation system furthercomprises one or more sensors configured to detect one or more flightparameters of the rotorcraft to form sensor data and a poweranticipation module configured to generate the power adjustment signalfor the first engine and to provide the second engine with a power inputstate change signal responsive to the sensor data.
 8. The powermanagement system as recited in claim 7 wherein the sensor data furthercomprises collective control data.
 9. The power management system asrecited in claim 7 wherein the sensor data further comprises firstengine speed data.
 10. The power management system as recited in claim 7wherein the sensor data further comprises first engine torque outputdata.
 11. The power management system as recited in claim 7 wherein thepower anticipation module is implemented on a flight control computer.12. The power management system as recited in claim 1 wherein the poweradjustment signal causes the first engine to reduce the first powerinput coincident with the power input step changes from the zero powerinput state to the positive power input state.
 13. The power managementsystem as recited in claim 1 wherein the power adjustment signal causesthe first engine to increase the first power input coincident with thepower input step changes from the positive power input state to the zeropower input state.
 14. The power management system as recited in claim 1wherein the power adjustment signal causes an adjustment in the quantityof fuel injected into the first engine.
 15. The power management systemas recited in claim 1 wherein the positive power input state furthercomprises a full power input state.
 16. The power management system asrecited in claim 1 wherein the power adjustment signal is mechanicallycoupled to the first engine.
 17. The power management system as recitedin claim 1 wherein the power adjustment signal is electrically coupledto the first engine.
 18. The power management system as recited in claim1 wherein the predetermined rotor speed threshold range is two percentabove and two percent below the main rotor speed.
 19. The powermanagement system as recited in claim 1 wherein the predetermined rotorspeed threshold range is one percent above and one percent below themain rotor speed.
 20. A rotorcraft comprising: a fuselage; a main rotorsystem rotatable relative to the fuselage, the main rotor system havinga main rotor speed; a first engine providing a first power input to themain rotor system; a second engine selectively providing a second powerinput to the main rotor system, the second engine having at least a zeropower input state and a positive power input state; a combining gearboxcoupling the first and second engines to the main rotor system; a spragclutch having an input side coupled to the second engine and an outputside coupled to the combining gearbox, the sprag clutch configured togenerate power input step changes between the zero power input state andthe positive power input state when a rotating speed of the input sidetransitions above or below a rotating speed of the output side; and apower anticipation system configured to provide the first engine with apower adjustment signal in anticipation of the power input step changes;wherein, the power adjustment signal causes the first engine to adjustthe first power input coincident with the power input step changes tomaintain the main rotor speed within a predetermined rotor speedthreshold range.